Scarlet Hedge works really nicely.
The flow is great with Summer in the middle spot and I don't think it's too much of an issue to have Summer Hedge either. It's not like using Rose Bush, as it's not.. an actual thing people say. (At least I've never heard anyone talk about summer hedges)
As for Palmer, it's all boy to me and Heidi Hedge sounds like a cartoon character (Bugs Bunny, Mickey Mouse, Daffy Duck) which I think is only due to the alliteration because I like Heidi in general.

Ultimately, go with what you like and not what a bunch of people over the internet told you. If you use a name you don't love you'll regret it. (Obviously also try to choose something reasonable but thats subjective).